The present disclosure relates to a method of producing a composite for acid gas separation, the composite having a function of separating an acid gas, and an apparatus for producing the same.
In recent years, development has advanced in techniques for selectively separating an acid gas in a mixed gas. In particular, the development has advanced in a technique for selectively separating carbon dioxide. As global warming countermeasures, for example, a technique has been developed in which carbon dioxide in an exhaust gas is recovered and concentrated, or hydrocarbon is reformed into hydrogen and carbon monoxide (CO) by steam reforming, and further allowing carbon monoxide to react with steam to produce carbon dioxide and hydrogen, and carbon dioxide is eliminated by a membrane through which carbon dioxide is selectively transmitted to obtain a gas containing as a main component hydrogen and for fuel cells or the like.
Meanwhile, with regard to separation of carbon dioxide, an amine absorption method has been general and widely applied, in which adsorption and desorption by amines are repeated. However, this method has disadvantages of needing a vast area for installing facilities, and also needing repetition of pressure increase/decrease and temperature rise/drop during adsorption/desorption to require a large amount of energy. Moreover, system capacity has been determined during design, and expansion or reduction of once established system capacity is far from easy. In contrast, a membrane separation method naturally causes separation depending on partial pressure of carbon dioxide in two regions divided by a separation membrane, and has advantages of small energy consumption and a compact installation area. Moreover, expansion or reduction of the system capacity can also be attained by increase or decrease in filter units. Therefore, a system having excellent scalability can be formed, and has recently attracted attention.
Composites for carbon dioxide separation used in the membrane separation method are generally classified into a so-called facilitated transport membrane in which a carbon dioxide carrier is contained in a carbon dioxide separation layer on a support, and carbon dioxide is transported on a side opposite to the membrane by this carrier, and a so-called dissolution diffusion membrane in which separation is performed by utilizing differences in solubility and diffusivity into the membrane between carbon dioxide and a separation target gas other than carbon dioxide (hereinafter, simply referred to as “separation target substance”) relative to the carbon dioxide separation layer.
In the dissolution diffusion membrane, the separation is performed based on the differences in the solubility into the membrane and the diffusivity into the membrane between carbon dioxide and the separation target substance. Therefore, if material and physical properties of the membrane are determined, a degree of separation is primarily determined, and accordingly as a membrane thickness becomes smaller, a rate of transmission of the mixed gas becomes larger. Therefore, the dissolution diffusion membrane is generally produced in the form of a thin film having a thickness of 1 μm or less by applying a producing method such as a layer separation method and an interfacial polymerization method.
In contrast, in the facilitated transport membrane, the solubility of carbon dioxide is significantly increased by the carbon dioxide carrier in the membrane and carbon dioxide is transported in the membrane with a high concentration. Therefore, the membrane generally has features of a higher degree of separation of carbon dioxide separation relative to the separation target substance in comparison with the dissolution diffusion membrane, and a larger rate of transmission of carbon dioxide. Moreover, a carbon dioxide concentration in the membrane is high, and thus a rate of diffusion of carbon dioxide in the membrane rarely serves as a rate-determining factor, and therefore in view of increasing the degree of separation relative to the separation target substance, the membrane is preferably formed into a thick film having a thickness of 10 μm or more.
For example, Japanese Examined Patent Publication No. 7(1995)-102310 (hereinafter, Patent Document 1) describes a method of producing a composite for carbon dioxide separation, in which an aqueous solution of uncrosslinked vinyl alcohol-acrylate copolymer is coated onto a carbon dioxide-permeable support in a membrane shape to form a liquid membrane of the aqueous solution of uncrosslinked vinyl alcohol-acrylate copolymer on the support, and then the liquid membrane is heated to cause crosslinking to form a water-insolubilized membrane, and an aqueous solution containing a carbon dioxide carrier (substance having affinity with carbon dioxide) is absorbed into the water-insolubilized membrane to produce a hydrogel membrane.
Japanese Unexamined Patent Publication No. 2012-143711 (hereinafter, Patent Document 2) describes a method of producing a composite for carbon dioxide separation, in which a gelling agent such as agar is added to a coating liquid containing a polyvinyl alcohol-polyacrylic acid copolymer and alkali metal carbonate, the coating liquid prepared at 50° C. or higher is coated onto a support, and then the resultant liquid membrane is cooled to cause hardening.